Go to a doctor.
Mood swings may be a sign of a mental health complication, but there may be other causes as well- my friend who had a thyroid problem used to have horrible mood swings, and they did some tests and found out what was wrong... he takes meds for it now and it's much better.
It's important to go to your doctor even when the concern *appears* to be just psychological, because it could be any number of things.
If you can afford it, go! Even if they do find nothing wrong physically, they can refer you to a mental health specialist.